Refrigerant charge management systems and methods

ABSTRACT

The present disclosure relates to a passive refrigerant charge management system including a charge vessel configured to fluidly couple to a refrigerant circuit. The charge vessel includes a first portion having a compressible fluid and a second portion configured to contain refrigerant of the refrigerant circuit, wherein an amount of the refrigerant contained in the second portion is based on a first pressure of the refrigerant within the refrigerant circuit and a second pressure of the compressible fluid.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Non-Provisional Application claiming priority toU.S. Provisional Application No. 62/639,875, entitled “REFRIGERANTCHARGE MANAGEMENT SYSTEMS AND METHODS,” filed Mar. 7, 2018, which ishereby incorporated by reference in its entirety for all purposes.

BACKGROUND

The present disclosure relates generally to heating, ventilation, andair conditioning systems. A wide range of applications exist forheating, ventilating, and air conditioning (HVAC) systems. For example,residential, light commercial, commercial, and industrial systems areused to control temperatures and air quality in residences andbuildings. Such systems often are dedicated to either heating orcooling, although systems are common that perform both of thesefunctions. Very generally, these systems operate by implementing athermal cycle in which fluids are heated and cooled to provide thedesired temperature in a controlled space, typically the inside of aresidence or building. Similar systems are used for vehicle heating andcooling, and as well as for general refrigeration. Many HVAC systems mayutilize fans, or blowers, in operation. For example, fans may be usedfor expelling exhaust air, moving air through a heat exchanger, anddrawing in return air. In certain instances, the HVAC system may have anoptimal or desired charge level of refrigerant to operate efficiently.However, the optimal charge level may vary based on a mode of the HVACsystem, such as a heating or cooling mode, an ambient temperature, apressure of the refrigerant within the HVAC system, among other factorsand parameters. However, in some instances, the charge level of the HVACsystem may be static or difficult to change.

SUMMARY

The present disclosure relates to a passive refrigerant chargemanagement system including a charge vessel configured to fluidly coupleto a refrigerant circuit. The charge vessel includes a first portionhaving a compressible fluid and a second portion configured to containrefrigerant of the refrigerant circuit, wherein an amount of therefrigerant contained in the second portion is based on a first pressureof the refrigerant within the refrigerant circuit and a second pressureof the compressible fluid.

The present disclosure also relates to a heating, ventilation, and airconditioning (HVAC) system having a refrigerant circuit configured toflow a refrigerant and a charge vessel fluidly coupled to therefrigerant circuit, wherein the charge vessel is configured topassively adjust a refrigerant charge level of the refrigerant circuitbased on a pressure of the refrigerant within the refrigerant circuit.

The present disclosure further relates to a heating, ventilation, andair conditioning (HVAC) system having a refrigerant loop, a condenserdisposed along the refrigerant loop and configured to condenserefrigerant of the refrigerant loop, and a charge vessel disposed alongthe refrigerant loop and configured to passively adjust a refrigerantcharge of the refrigerant loop based on a discharge pressure of therefrigerant from the condenser.

DRAWINGS

FIG. 1 is a perspective view of a heating, ventilating, and airconditioning (HVAC) system for building environmental management thatmay employ one or more HVAC units, in accordance with an embodiment ofthe present disclosure;

FIG. 2 is a perspective view of an HVAC unit of the HVAC system of FIG.1, in accordance with an embodiment of the present disclosure;

FIG. 3 is a perspective view of a residential split heating and coolingsystem, in accordance with an embodiment of the present disclosure;

FIG. 4 is a schematic view of a vapor compression system that may beused in an HVAC system, in accordance with an embodiment of the presentdisclosure;

FIG. 5 is a schematic view of a heat pump system having a passive chargemanagement system, in accordance with an embodiment of the presentdisclosure;

FIG. 6 is a schematic view of an air conditioning system having apassive charge management system, in accordance with an embodiment ofthe present disclosure;

FIG. 7 is a schematic view of a charge vessel of the passive chargemanagement systems of FIGS. 5 and 6, in accordance with an embodiment ofthe present disclosure; and

FIG. 8 is a schematic view of a charge vessel of the passive chargemanagement systems of FIGS. 5 and 6, in accordance with an embodiment ofthe present disclosure.

DETAILED DESCRIPTION

Heating, ventilation, and air conditioning (HVAC) systems may include anoptimum or desired charge level, or a quantity of refrigerant, tooperate efficiently. However, the optimal or desired charge level mayfluctuate as an ambient temperature, a mode of the HVAC system, or arefrigerant pressure within the HVAC system changes. For example, as anoutdoor temperature increases, some amount of refrigerant may collect orbecome backed up in the condensing heat exchanger of the HVAC system.The HVAC system may increase an input power of a pump to process thecollected refrigerant, thereby decreasing an efficiency of the HVACsystem. Indeed, in such instances, a decreased charge level may increasean efficiency of the HVAC system. Similarly, as an outdoor temperaturedecreases, the amount of refrigerant that is collected or backed up inthe condensing heat exchanger may decrease. This may result in anincomplete column of liquid flowing to the expansion device from theheat exchanger, thereby decreasing an efficiency of the HVAC system.Indeed, in such instances, an increased charge level may increase anefficiency of the HVAC system.

Accordingly, the present disclosure is directed to heating, ventilation,and air conditioning (HVAC) systems and units, which may include apassive refrigerant charge management system. Particularly, the HVACsystems may include a charge vessel configured to accept varied amountsof refrigerant depending on conditions of the HVAC system and/orsurrounding environment. The charge vessel may be a rigid container thatis fluidly coupled to a liquid line of a refrigerant circuit of the HVACsystem. Moreover, the charge vessel may be divided into two sections: afirst section having a set amount of compressible fluid and a secondsection in fluid communication with liquid refrigerant of the HVACsystem and configured to accept various amounts of refrigerant. Theamount of refrigerant accepted in the second section may depend at leastin part on a pressure of the refrigerant within the liquid line portionof the refrigerant circuit. The first and second sections are dividedwithin the rigid container by a flexible divider, such as a bladder,membrane, or diaphragm. As discussed herein, the flexible divider mayexpand and contract in response to pressures of the refrigerant withinthe refrigerant circuit to adjust the refrigerant charge in therefrigerant circuit. For example, when the refrigerant pressure in therefrigerant loop is higher, the flexible membrane may deform to decreasea volume of the first section and thereby increase refrigerant chargeaccepted into the second section. Similarly, when the refrigerantpressure in the refrigerant loop is lower, the flexible membrane maydeform to increase a volume of the first section and thereby decreasethe refrigerant charge accepted into the second section. In otherembodiments, the divider may be passively biased by a mechanicalfeature, such as a spring or other mechanism that applies force whencompressed.

Turning now to the drawings, FIG. 1 illustrates a heating, ventilating,and air conditioning (HVAC) system for building environmental managementthat may employ one or more HVAC units. In the illustrated embodiment, abuilding 10 is air conditioned by a system that includes an HVAC unit12. The building 10 may be a commercial structure or a residentialstructure. As shown, the HVAC unit 12 is disposed on the roof of thebuilding 10; however, the HVAC unit 12 may be located in other equipmentrooms or areas adjacent the building 10. The HVAC unit 12 may be asingle package unit containing other equipment, such as a blower,integrated air handler, and/or auxiliary heating unit. In otherembodiments, the HVAC unit 12 may be part of a split HVAC system, suchas the system shown in FIG. 3, which includes an outdoor HVAC unit 58and an indoor HVAC unit 56.

The HVAC unit 12 is an air cooled device that implements a refrigerationcycle to provide conditioned air to the building 10. Specifically, theHVAC unit 12 may include one or more heat exchangers across which an airflow is passed to condition the air flow before the air flow is suppliedto the building. In the illustrated embodiment, the HVAC unit 12 is arooftop unit (RTU) that conditions a supply air stream, such asenvironmental air and/or a return air flow from the building 10. Afterthe HVAC unit 12 conditions the air, the air is supplied to the building10 via ductwork 14 extending throughout the building 10 from the HVACunit 12. For example, the ductwork 14 may extend to various individualfloors or other sections of the building 10. In certain embodiments, theHVAC unit 12 may be a heat pump that provides both heating and coolingto the building with one refrigeration circuit configured to operate indifferent modes. In other embodiments, the HVAC unit 12 may include oneor more refrigeration circuits for cooling an air stream and a furnacefor heating the air stream.

A control device 16, one type of which may be a thermostat, may be usedto designate the temperature of the conditioned air. The control device16 also may be used to control the flow of air through the ductwork 14.For example, the control device 16 may be used to regulate operation ofone or more components of the HVAC unit 12 or other components, such asdampers and fans, within the building 10 that may control flow of airthrough and/or from the ductwork 14. In some embodiments, other devicesmay be included in the system, such as pressure and/or temperaturetransducers or switches that sense the temperatures and pressures of thesupply air, return air, and so forth. Moreover, the control device 16may include computer systems that are integrated with or separate fromother building control or monitoring systems, and even systems that areremote from the building 10.

FIG. 2 is a perspective view of an embodiment of the HVAC unit 12. Inthe illustrated embodiment, the HVAC unit 12 is a single package unitthat may include one or more independent refrigeration circuits andcomponents that are tested, charged, wired, piped, and ready forinstallation. The HVAC unit 12 may provide a variety of heating and/orcooling functions, such as cooling only, heating only, cooling withelectric heat, cooling with dehumidification, cooling with gas heat, orcooling with a heat pump. As described above, the HVAC unit 12 maydirectly cool and/or heat an air stream provided to the building 10 tocondition a space in the building 10.

As shown in the illustrated embodiment of FIG. 2, a cabinet 24 enclosesthe HVAC unit 12 and provides structural support and protection to theinternal components from environmental and other contaminants. In someembodiments, the cabinet 24 may be constructed of galvanized steel andinsulated with aluminum foil faced insulation. Rails 26 may be joined tothe bottom perimeter of the cabinet 24 and provide a foundation for theHVAC unit 12. In certain embodiments, the rails 26 may provide accessfor a forklift and/or overhead rigging to facilitate installation and/orremoval of the HVAC unit 12. In some embodiments, the rails 26 may fitinto “curbs” on the roof to enable the HVAC unit 12 to provide air tothe ductwork 14 from the bottom of the HVAC unit 12 while blockingelements such as rain from leaking into the building 10.

The HVAC unit 12 includes heat exchangers 28 and 30 in fluidcommunication with one or more refrigeration circuits. Tubes within theheat exchangers 28 and 30 may circulate refrigerant, such as R-410A,through the heat exchangers 28 and 30. The tubes may be of varioustypes, such as multichannel tubes, conventional copper or aluminumtubing, and so forth. Together, the heat exchangers 28 and 30 mayimplement a thermal cycle in which the refrigerant undergoes phasechanges and/or temperature changes as it flows through the heatexchangers 28 and 30 to produce heated and/or cooled air. For example,the heat exchanger 28 may function as a condenser where heat is releasedfrom the refrigerant to ambient air, and the heat exchanger 30 mayfunction as an evaporator where the refrigerant absorbs heat to cool anair stream. In other embodiments, the HVAC unit 12 may operate in a heatpump mode where the roles of the heat exchangers 28 and 30 may bereversed. That is, the heat exchanger 28 may function as an evaporatorand the heat exchanger 30 may function as a condenser. In furtherembodiments, the HVAC unit 12 may include a furnace for heating the airstream that is supplied to the building 10. While the illustratedembodiment of FIG. 2 shows the HVAC unit 12 having two of the heatexchangers 28 and 30, in other embodiments, the HVAC unit 12 may includeone heat exchanger or more than two heat exchangers.

The heat exchanger 30 is located within a compartment 31 that separatesthe heat exchanger 30 from the heat exchanger 28. Fans 32 draw air fromthe environment through the heat exchanger 28. Air may be heated and/orcooled as the air flows through the heat exchanger 28 before beingreleased back to the environment surrounding the rooftop unit 12. Ablower assembly 34, powered by a motor 36, draws air through the heatexchanger 30 to heat or cool the air. The heated or cooled air may bedirected to the building 10 by the ductwork 14, which may be connectedto the HVAC unit 12. Before flowing through the heat exchanger 30, theconditioned air flows through one or more filters 38 that may removeparticulates and contaminants from the air. In certain embodiments, thefilters 38 may be disposed on the air intake side of the heat exchanger30 to prevent contaminants from contacting the heat exchanger 30.

The HVAC unit 12 also may include other equipment for implementing thethermal cycle. Compressors 42 increase the pressure and temperature ofthe refrigerant before the refrigerant enters the heat exchanger 28. Thecompressors 42 may be any suitable type of compressors, such as scrollcompressors, rotary compressors, screw compressors, or reciprocatingcompressors. In some embodiments, the compressors 42 may include a pairof hermetic direct drive compressors arranged in a dual stageconfiguration 44. However, in other embodiments, any number of thecompressors 42 may be provided to achieve various stages of heatingand/or cooling. As may be appreciated, additional equipment and devicesmay be included in the HVAC unit 12, such as a solid-core filter drier,a drain pan, a disconnect switch, an economizer, pressure switches,phase monitors, and humidity sensors, among other things.

The HVAC unit 12 may receive power through a terminal block 46. Forexample, a high voltage power source may be connected to the terminalblock 46 to power the equipment. The operation of the HVAC unit 12 maybe governed or regulated by a control board 48. The control board 48 mayinclude control circuitry connected to a thermostat, sensors, andalarms. One or more of these components may be referred to hereinseparately or collectively as the control device 16. The controlcircuitry may be configured to control operation of the equipment,provide alarms, and monitor safety switches. Wiring 49 may connect thecontrol board 48 and the terminal block 46 to the equipment of the HVACunit 12.

FIG. 3 illustrates a residential heating and cooling system 50, also inaccordance with present techniques. The residential heating and coolingsystem 50 may provide heated and cooled air to a residential structure,as well as provide outside air for ventilation and provide improvedindoor air quality (IAQ) through devices such as ultraviolet lights andair filters. In the illustrated embodiment, the residential heating andcooling system 50 is a split HVAC system. In general, a residence 52conditioned by a split HVAC system may include refrigerant conduits 54that operatively couple the indoor unit 56 to the outdoor unit 58. Theindoor unit 56 may be positioned in a utility room, an attic, abasement, and so forth. The outdoor unit 58 is typically situatedadjacent to a side of residence 52 and is covered by a shroud to protectthe system components and to prevent leaves and other debris orcontaminants from entering the unit. The refrigerant conduits 54transfer refrigerant between the indoor unit 56 and the outdoor unit 58,typically transferring primarily liquid refrigerant in one direction andprimarily vaporized refrigerant in an opposite direction.

When the system shown in FIG. 3 is operating as an air conditioner, aheat exchanger 60 in the outdoor unit 58 serves as a condenser forre-condensing vaporized refrigerant flowing from the indoor unit 56 tothe outdoor unit 58 via one of the refrigerant conduits 54. In theseapplications, a heat exchanger 62 of the indoor unit functions as anevaporator. Specifically, the heat exchanger 62 receives liquidrefrigerant (which may be expanded by an expansion device, not shown)and evaporates the refrigerant before returning it to the outdoor unit58.

The outdoor unit 58 draws environmental air through the heat exchanger60 using a fan 64 and expels the air above the outdoor unit 58. Whenoperating as an air conditioner, the air is heated by the heat exchanger60 within the outdoor unit 58 and exits the unit at a temperature higherthan it entered. The indoor unit 56 includes a blower or fan 66 thatdirects air through or across the indoor heat exchanger 62, where theair is cooled when the system is operating in air conditioning mode.Thereafter, the air is passed through ductwork 68 that directs the airto the residence 52. The overall system operates to maintain a desiredtemperature as set by a system controller. When the temperature sensedinside the residence 52 is higher than the set point on the thermostat,or the set point plus a small amount, the residential heating andcooling system 50 may become operative to refrigerate additional air forcirculation through the residence 52. When the temperature reaches theset point, or the set point minus a small amount, the residentialheating and cooling system 50 may stop the refrigeration cycletemporarily.

The residential heating and cooling system 50 may also operate as a heatpump. When operating as a heat pump, the roles of heat exchangers 60 and62 are reversed. That is, the heat exchanger 60 of the outdoor unit 58will serve as an evaporator to evaporate refrigerant and thereby coolair entering the outdoor unit 58 as the air passes over outdoor the heatexchanger 60. The indoor heat exchanger 62 will receive a stream of airblown over it and will heat the air by condensing the refrigerant.

In some embodiments, the indoor unit 56 may include a furnace system 70.For example, the indoor unit 56 may include the furnace system 70 whenthe residential heating and cooling system 50 is not configured tooperate as a heat pump. The furnace system 70 may include a burnerassembly and heat exchanger, among other components, inside the indoorunit 56. Fuel is provided to the burner assembly of the furnace 70 whereit is mixed with air and combusted to form combustion products. Thecombustion products may pass through tubes or piping in a heatexchanger, separate from heat exchanger 62, such that air directed bythe blower 66 passes over the tubes or pipes and extracts heat from thecombustion products. The heated air may then be routed from the furnacesystem 70 to the ductwork 68 for heating the residence 52.

FIG. 4 is an embodiment of a vapor compression system 72 that can beused in any of the systems described above. The vapor compression system72 may circulate a refrigerant through a circuit starting with acompressor 74. The circuit may also include a condenser 76, an expansionvalve(s) or device(s) 78, and an evaporator 80. The vapor compressionsystem 72 may further include a control panel 82 that has an analog todigital (A/D) converter 84, a microprocessor 86, a non-volatile memory88, and/or an interface board 90. The control panel 82 and itscomponents may function to regulate operation of the vapor compressionsystem 72 based on feedback from an operator, from sensors of the vaporcompression system 72 that detect operating conditions, and so forth.

In some embodiments, the vapor compression system 72 may use one or moreof a variable speed drive (VSDs) 92, a motor 94, the compressor 74, thecondenser 76, the expansion valve or device 78, and/or the evaporator80. The motor 94 may drive the compressor 74 and may be powered by thevariable speed drive (VSD) 92. The VSD 92 receives alternating current(AC) power having a particular fixed line voltage and fixed linefrequency from an AC power source, and provides power having a variablevoltage and frequency to the motor 94. In other embodiments, the motor94 may be powered directly from an AC or direct current (DC) powersource. The motor 94 may include any type of electric motor that can bepowered by a VSD or directly from an AC or DC power source, such as aswitched reluctance motor, an induction motor, an electronicallycommutated permanent magnet motor, or another suitable motor.

The compressor 74 compresses a refrigerant vapor and delivers the vaporto the condenser 76 through a discharge passage. In some embodiments,the compressor 74 may be a centrifugal compressor. The refrigerant vapordelivered by the compressor 74 to the condenser 76 may transfer heat toa fluid passing across the condenser 76, such as ambient orenvironmental air 96. The refrigerant vapor may condense to arefrigerant liquid in the condenser 76 as a result of thermal heattransfer with the environmental air 96. The liquid refrigerant from thecondenser 76 may flow through the expansion device 78 to the evaporator80.

The liquid refrigerant delivered to the evaporator 80 may absorb heatfrom another air stream, such as a supply air stream 98 provided to thebuilding 10 or the residence 52. For example, the supply air stream 98may include ambient or environmental air, return air from a building, ora combination of the two. The liquid refrigerant in the evaporator 80may undergo a phase change from the liquid refrigerant to a refrigerantvapor. In this manner, the evaporator 38 may reduce the temperature ofthe supply air stream 98 via thermal heat transfer with the refrigerant.Thereafter, the vapor refrigerant exits the evaporator 80 and returns tothe compressor 74 by a suction line to complete the cycle.

In some embodiments, the vapor compression system 72 may further includea reheat coil in addition to the evaporator 80. For example, the reheatcoil may be positioned downstream of the evaporator relative to thesupply air stream 98 and may reheat the supply air stream 98 when thesupply air stream 98 is overcooled to remove humidity from the supplyair stream 98 before the supply air stream 98 is directed to thebuilding 10 or the residence 52.

It should be appreciated that any of the features described herein maybe incorporated with the HVAC unit, the residential heating and coolingsystem 50, or other HVAC systems. Additionally, while the featuresdisclosed herein are described in the context of embodiments thatdirectly heat and cool a supply air stream provided to a building orother load, embodiments of the present disclosure may be applicable toother HVAC systems as well. For example, the features described hereinmay be applied to mechanical cooling systems, free cooling systems,chiller systems, or other heat pump or refrigeration applications.

As set forth above, embodiments of the present disclosure are directedto a passive charge management system of the HVAC unit 12, theresidential heating and cooling system 50, and/or the vapor compressionsystem 72, any of which may referred to as an HVAC system 100. Forexample, FIGS. 5 and 6 are embodiments of a heat pump system 102 of theHVAC system 100 and of an air conditioning system 103 of the HVAC system100, respectively, which may utilize a passive charge vessel 105 topassively manage the charge level of the HVAC system 100.

To illustrate, the following discussion focuses on FIG. 5, which is aschematic representation of the heat pump system 102 of the HVAC system100. In certain embodiments, the heat pump system 102 may include areversing valve 106, such as a four-way valve. Thus, the HVAC system 100may include the indoor HVAC unit 56 having the heat exchanger 62discussed above, such as an indoor heat exchanger 108, and the outdoorHVAC unit 58 having the heat exchanger 60 discussed above, such as anoutdoor heat exchanger 110. A compressor, such as the compressor 74discussed above, along with the reversing valve 106, may be selectivelyactuated to drive refrigerant through a refrigerant circuit 112 in afirst direction 120. Similarly, the compressor 74 and the reversingvalve 106 may be selectively actuated to drive refrigerant through therefrigerant circuit 112 in a second direction 122, opposite of the firstdirection 120.

Under conditions in which the refrigerant flows from the indoor heatexchanger 108 to the outdoor heat exchanger 110 in the first direction120, the HVAC system 100 may activate the fan 64 to evaporaterefrigerant within the outdoor heat exchanger 110 and activate theblower 66 to pass air over the indoor heat exchanger 108, whichcondenses the refrigerant. Thus, the air passing over the indoor heatexchanger 108 is heated and provided to an interior space of thebuilding 10 or residence 52. When the refrigerant flows in the seconddirection 122 from the outdoor heat exchanger 110 to the indoor heatexchanger 108, the indoor heat exchanger 108 alternatively operates asan evaporator, thus enabling the HVAC system 100 provide cooled air tothe interior space of the building 10 or residence 52. Moreover, anexpansion valve, such as the expansion device 78, is shown between theindoor heat exchanger 108 and the outdoor heat exchanger 110.Particularly, a first expansion device 124 may be utilized while therefrigerant is flowing in the first direction 120 and a second expansiondevice 126 may be utilized while the refrigerant is flowing in thesecond direction 122. The first and second expansion devices 124, 126may also utilize a first one-way valve 128 and a second one-way valve130, respectively, depending on a direction of flow of the refrigerantthrough the heat pump system 102. For example, when the refrigerantflows in the first direction 120, the refrigerant may flow through thesecond one-way valve 130 and through the first expansion device 124.When the refrigerant flows in the second direction 122, the refrigerantmay flow through the first one-way valve 128 and through the secondexpansion device 126.

The following discussion focuses on FIG. 6, which is a schematic view ofan embodiment of the air conditioning system 103 of an embodiment of theHVAC system 100. The air conditioning system 103 may function in amanner similar to the heat pump system 102 when the refrigerant withinthe heat pump system 102 flows in the second direction 122 and/or to thevapor compression system 72 of FIG. 4. That is, the air conditioningsystem 103 may utilize the outdoor heat exchanger 110, the expansiondevice 78, the indoor heat exchanger 108, and the compressor 74. Forexample, the compressor 74 may compress the refrigerant and deliver itto the outdoor heat exchanger 110, which functions as a condenser.Indeed, the outdoor heat exchanger 110 may condense the refrigerant to aliquid state. From the outdoor heat exchanger 110, the refrigerant mayflow through the expansion device 78 to the indoor heat exchanger 108,which functions as an evaporator. Indeed, the refrigerant may undergo aphase change from a liquid state to a vaporous state as the refrigerantflows through the indoor heat exchanger 108. From the indoor heatexchanger 108, the refrigerant may flow to the compressor 74 to continuethrough the refrigerant circuit 112.

Further, in both FIGS. 5 and 6, the HVAC system 100 includes the chargevessel 105 configured to accept varying amounts of refrigerant, orcharge, from the HVAC system 100, depending at least in part on apressure of the refrigerant within the HVAC system 100. First, it shouldbe noted that a charge level of refrigerant may refer to the quantity ofrefrigerant within a system. Further, an optimum, desired, or targetcharge level of the HVAC system 100 may depend on various conditions ofthe HVAC system 100, such as ambient temperatures and/or a mode of theHVAC system 100. Indeed, as mentioned above, an efficiency of the HVACsystem 100 may benefit from having a decreased charge level when theambient temperature is high and may benefit from having an increasedcharge level when the ambient temperature is low. Moreover, a dischargepressure of the HVAC system 100 may be affected by the ambienttemperatures. As used herein, the discharge pressure may refer to thepressure of the refrigerant in the refrigerant circuit 112 after beingdischarged from the compressor 74. Further, it is to be understood thatthe discharge pressure of the condenser 74 may be positively correlatedto refrigerant pressures throughout the refrigerant circuit 112 beforethe expansion device. Therefore, discussions of trends, such asincreases or decreases, of the discharge pressure from the compressor 74may also refer to corresponding trends of pressures throughout therefrigerant circuit 112 before the expansion device, and morespecifically, to refrigerant pressures located downstream of thecondensing heat exchanger, where the charge vessel 105 may be fluidlycoupled. Indeed, it is to be further understood that, in certainembodiments, the discharge pressure may refer to the pressure downstreamof the condensing heat exchanger.

In the heat pump system 102, the outdoor heat exchanger 110 may functionas the condensing heat exchanger when the refrigerant is flowing in thesecond direction 122. Correspondingly, the indoor heat exchanger 108 mayfunction as a condensing heat exchanger when the refrigerant is flowingin the first direction 120. Further, in the air conditioning system 103,the outdoor heat exchanger 110 may always function as a condensing heatexchanger while the air conditioning system 103 is in operation. Incertain embodiments, the charge vessel 105 may be located within theoutdoor HVAC unit 58 when the HVAC system 100 is a split HVAC system,such as the system shown in FIG. 3.

When the ambient temperature is high, the discharge pressure of the HVACsystem 100 may increase. Similarly, when ambient temperatures are low,the discharge pressure of the HVAC system 100 may decrease. For example,as discussed above, when the ambient temperature increases, excessrefrigerant may gather at the condensing heat exchanger, and the HVACsystem 100 may increase a power input to the compressor 74, therebyincreasing the discharge pressure. Similarly, when the ambienttemperature decreases, the condensing heat exchanger may output anincomplete column of liquid refrigerant, thereby decreasing dischargepressure. Indeed, the HVAC system 100 may benefit from a decreasedcharge level when the ambient temperature is high and may benefit froman increased charge level when the ambient temperature are low.Therefore, the charge vessel 105 is configured to remove refrigerantcharge from the refrigerant circuit when the discharge pressure is highand to add refrigerant charge when the discharge pressure is low.

To this end, the charge vessel 105 is divided into a first section 142,which contains a compressible fluid, and a second section 144, which isin fluid communication with the liquid refrigerant of the refrigerantloop 112. The first section 142 may be fluidly isolated from the secondsection 144 and may contain a pre-determined amount of a compressiblefluid, such as an inert gas. Indeed, the first section 142 may includenitrogen, helium, neon, argon, any combination thereof, or any othersuitable compressible fluid. The first section 142 and the secondsection 144 may be separated by a divider 146, such as a bladder, amembrane, and/or a diaphragm. Therefore, as the discharge pressure ofthe HVAC system 100 increases, the charge vessel 105 may accept anincreased amount of refrigerant, or charge, into the second section 144.

The pressures of first section 142 and the second section 144 aresubstantially in equilibrium while the volumes of the first section 142and the second section 144 are inversely related. To elaborate, as thedischarge pressure increases, the pressure within the second section 144correspondingly increases, thereby flexing the divider 146 to increase avolume of the second section 144. As a result, a volume of the firstsection 142 decreases, which increases a pressure of the first section142 to substantially match the pressure within the second section 144.Similarly, as the discharge pressure decreases, the pressure within thesecond section 144 correspondingly decreases, thereby flexing thedivider 146 to decrease a volume of the second section 144. Thus, avolume of the first section 142 increases, which decreases a pressure ofthe first section 142 to substantially match the pressure within thefirst section 144.

To help illustrate, FIGS. 7 and 8 are schematic diagrams of a crosssection of the charge vessel 105 when the discharge pressure is high andwhen the discharge pressure is low, respectively. As discussed herein,the charge vessel 105 may passively manage the charge within therefrigerant loop 112 of the HVAC system 100. In other words, the chargevessel 105 may add or withdraw charge from the HVAC system 100 in directresponse to, or as a direct result of, a changing discharge pressurewithin the HVAC system 100. Indeed, the amount of refrigerant added orwithdrawn from the system may be directly proportional to the dischargepressure. For example, as discussed above, as the discharge pressureincreases, the amount of refrigerant contained within the second section144 may proportionally increase. Similarly, as the discharge pressuredecreases, the amount of refrigerant contained within the second section144 may proportionally decrease. Further, it should be understood that,in some embodiments, the amount of refrigerant added or withdrawn fromthe HVAC system 100 or charge vessel 105 may also be at least partiallydependent on an elasticity of the divider 146.

As shown, the first and section sections 142, 144 may be containedwithin a rigid outer shell 150 and are separated by the divider 146. Incertain embodiments, the compressible fluid contained within the firstsection 142 may be completely encapsulated by the divider 146. That is,the divider 146 may function as an elastic sac/bladder that lines theinterior surface of the first section 142 of the charge vessel 105. Insome embodiments, the compressible fluid of the first section 142 may becontained by, and in contact with, both an interior surface of thecharge vessel 105, such as an interior surface of the shell 150, and thedivider 146. For example, in such embodiments, the divider 146 may becoupled to the interior surface of the charge vessel 105 along a line152.

Further, the charge vessel 105 may be in fluid communication with therefrigerant loop of the HVAC system 100 via a conduit 154. Morespecifically, the conduit 154 may fluidly couple the charge vessel 105to a liquid refrigerant portion 155 of the refrigerant loop 112, whichmay substantially contain liquid refrigerant due at least in part to itsdownstream position relative to the condensing heat exchanger. To thisend, the charge vessel 105 may be configured to accept refrigerant thatis substantially in the liquid phase. In this manner, the charge vessel105 is configured to accept a greater mass of refrigerant than if thecharge vessel 105 was in fluid communication with a portion of the HVACsystem 100 containing vapor refrigerant. In some embodiments, theconduit 154 may be coupled to a corresponding conduit of the refrigerantcircuit 112 at a bottom of the corresponding conduit. Therefore, thecharge vessel 105 may receive less vapor refrigerant in embodimentswhere vapor refrigerant is present because the liquid refrigerant maytend to be disposed lower in the corresponding conduit, as liquidrefrigerant is denser than vapor refrigerant. In some embodiments, thecharge vessel 105 is configured to hold approximately 10 to 20% of thetotal charge of the HVAC system 100. In some embodiments, the chargevessel 105 is configured to hold approximately 1 to 2 pounds ofrefrigerant.

In certain embodiments, the conduit 154 may include a valve 156, such asa shut-off valve, which may close to separate the charge vessel 105 fromthe refrigerant circuit 112. Further, in some embodiments, the chargevessel 105 may include a pressure sensor 160 configured tomeasure/detect/determine a pressure within the charge vessel 105, andmore specifically, within the first section 142 and/or the secondsection 144. The valve 156 and the pressure sensor 160 may becommunicatively coupled to a controller 162, such as the control panel82. The controller 162 may include a processor 164, which may representone or more processors, such as an application-specific processor. Thecontroller 162 may also include a memory device 166 for storinginstructions executable by the processor 166 to perform the methods andcontrol actions described herein for the HVAC system 100. The processor164 may include one or more processing devices, and the memory 166 mayinclude one or more tangible, non-transitory, machine-readable media. Byway of example, such machine-readable media can include RAM, ROM, EPROM,EEPROM, CD-ROM, or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium which can be used tocarry or store desired program code in the form of machine-executableinstructions or data structures and which can be accessed by theprocessor 164 or by any general purpose or special purpose computer orother machine with a processor. In certain embodiments, the controller162 may keep the valve 156 open while the pressure of the charge vessel105 is within a minimum and maximum threshold pressure range. That is,if the pressure of the charge vessel 105 exceeds the maximum thresholdor falls below the minimum threshold, the controller 162 may actuate thevalve 156 to seal the charge vessel 105 from the refrigerant circuit 112of the HVAC system 100.

Accordingly, the present disclosure is directed to providing systems andmethods for passive refrigerant charge management. Particularly,heating, ventilation, and air conditioning (HVAC) systems may include acharge vessel fluidly coupled to the refrigerant circuit of the HVACsystem. The charge vessel includes a first portion having a compressiblefluid and a second portion fluidly coupled with the refrigerant circuitand configured to accept various amounts of refrigerant in response to apressure within the refrigerant circuit to increase an efficiency of theHVAC system. The pressure of the refrigerant within the refrigerantcircuit may depend on an ambient temperature of the HVAC system. Keepingthis in mind, as the ambient temperature changes, the optimal, target,or desired charge level of the HVAC system may also change.Particularly, as the ambient temperature increases, the desired chargelevel may decrease and as the ambient temperature decreases, the desiredcharge level may increase. Therefore, the charge vessel is configured toincrease efficiency of the HVAC system by automatically removingrefrigerant charge from the refrigerant circuit as the ambienttemperature increases and by automatically adding refrigerant charge tothe refrigerant circuit as the ambient temperature decreases.

While only certain features and embodiments of the present disclosurehave been illustrated and described, many modifications and changes mayoccur to those skilled in the art, such as variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, such as temperatures or pressures, mountingarrangements, use of materials, colors, orientations, and so forth,without materially departing from the novel teachings and advantages ofthe subject matter recited in the claims. The order or sequence of anyprocess or method steps may be varied or re-sequenced according toalternative embodiments. It is, therefore, to be understood that theappended claims are intended to cover all such modifications and changesas fall within the true spirit of the present disclosure. Furthermore,in an effort to provide a concise description of the exemplaryembodiments, all features of an actual implementation may not have beendescribed, such as those unrelated to the presently contemplated bestmode of carrying out the present disclosure, or those unrelated toenabling the claimed embodiments. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation specific decisions may be made.Such a development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure, without undue experimentation.

1. A passive refrigerant charge management system, comprising: a chargevessel configured to fluidly couple to a refrigerant circuit, whereinthe charge vessel comprises: a first portion comprising a compressiblefluid; and a second portion configured to contain refrigerant of therefrigerant circuit, wherein an amount of the refrigerant contained inthe second portion is based on a first pressure of the refrigerantwithin the refrigerant circuit and a second pressure of the compressiblefluid.
 2. The passive refrigerant charge management system of claim 1,wherein the second portion is configured to fluidly couple to a liquidrefrigerant portion of the refrigerant circuit.
 3. The passiverefrigerant charge management system of claim 1, wherein the chargevessel comprises a flexible divider disposed between the first portionand the second portion, and wherein the flexible divider fluidlyseparates the first portion and the second portion.
 4. The passiverefrigerant charge management system of claim 3, wherein the flexibledivider comprises a bladder, and wherein the bladder contains thecompressible fluid.
 5. The passive refrigerant charge management systemof claim 1, wherein the charge vessel comprises a sensor configured tomeasure a fluid pressure within the charge vessel.
 6. The passiverefrigerant charge management system of claim 1, wherein thecompressible fluid comprises an inert gas.
 7. The passive refrigerantcharge management system of claim 1, wherein the second portion of thecharge vessel is configured to hold 10 to 20 percent of a totalrefrigerant charge of the refrigerant circuit.
 8. The passiverefrigerant charge management system of claim 1, wherein the chargevessel is configured to passively remove refrigerant charge from therefrigerant circuit as an ambient temperature increases and to passivelyadd refrigerant charge to the refrigerant circuit as the ambienttemperature decreases.
 9. A heating, ventilation, and air conditioning(HVAC) system, comprising: a refrigerant circuit configured to flow arefrigerant; and a charge vessel fluidly coupled to the refrigerantcircuit, wherein the charge vessel is configured to passively adjust arefrigerant charge level of the refrigerant circuit based on a pressureof the refrigerant within the refrigerant circuit.
 10. The HVAC systemof claim 9, comprising an indoor HVAC unit and an outdoor HVAC unit,wherein the outdoor HVAC unit comprises the charge vessel.
 11. The HVACsystem of claim 9, wherein the charge vessel comprises a shell and abladder disposed within the shell.
 12. The HVAC system of claim 9,wherein the charge vessel is fluidly coupled to a liquid refrigerantportion of the refrigerant circuit, wherein the liquid refrigerantportion is configured to flow substantially liquid refrigerant duringoperation of the HVAC system.
 13. The HVAC system of claim 9, whereinthe charge vessel comprises a first section comprising a compressiblefluid, and wherein the charge vessel comprises a second section fluidlycoupled to the refrigerant circuit, wherein the first section and secondsection are fluidly separate from one another.
 14. The HVAC system ofclaim 9, wherein the charge vessel comprises a flexible bladderconfigured to deform in response to the pressure of the refrigerant. 15.The HVAC system of claim 9, wherein the charge vessel is configured toautomatically accept refrigerant from the refrigerant circuit as thepressure increases and automatically discharge refrigerant to therefrigerant circuit as the pressure decreases.
 16. The HVAC system ofclaim 9, comprising a heat pump system, wherein the heat pump systemcomprises the refrigerant circuit.
 17. The HVAC system of claim 9,comprising an air conditioning system, wherein the air conditioningsystem comprises the refrigerant circuit.
 18. A heating, ventilation,and air conditioning (HVAC) system, comprising: a refrigerant loop; acondenser disposed along the refrigerant loop and configured to condenserefrigerant of the refrigerant loop; and a charge vessel disposed alongthe refrigerant loop and configured to passively adjust a refrigerantcharge of the refrigerant loop based on a discharge pressure of therefrigerant from the condenser.
 19. The HVAC system of claim 18, whereinthe charge vessel is fluidly coupled to the refrigerant loop at alocation along the refrigerant loop where the refrigerant at thelocation is substantially liquid.
 20. The HVAC system of claim 18,wherein the charge vessel comprises a bladder configured to passivelyflex to adjust the refrigerant charge of the refrigerant loop.
 21. TheHVAC system of claim 18, wherein the charge vessel comprises a fluidlyisolated portion configured to adjust in volume in response to thedischarge pressure.
 22. The HVAC system of claim 18, wherein the chargevessel comprises a section isolated from the refrigerant loop, whereinthe section comprises a compressible fluid.
 23. The HVAC system of claim22, wherein the compressible fluid comprises an inert gas.
 24. The HVACsystem of claim 18, wherein the charge vessel is configured to passivelyremove refrigerant charge from the refrigerant loop as an ambienttemperature increases and to passively add refrigerant charge to therefrigerant loop as the ambient temperature decreases.